Typical outerwear involves three layers of fabric: a waterproof outer shell, a warm layer of insulation, and an inside wicking layer. Insulating layers have been used for some time in articles of clothing to provide protection and comfort. The insulating layer, when used in combination with the overlaying outer shell, shields the user against uncomfortably cold or hot temperatures and high levels of moisture. Various insulating materials for insulating liners that have been used in the textile industry include felt, fleece, flannel, wool, various forms of latex foam, or the like. Although flexible and readily adaptable for textile applications, such materials are often provided in relatively thick slabs that can be bulky, thereby requiring the user, for example, to use a larger sized garment in order to fit the insulating material or liner. Also, such materials often do not exhibit effective insulative properties in extremely high or extremely low temperature environments.
Silica-based aerogels have been known to exhibit excellent thermal insulation performance, and have been readily adapted for use in high temperature thermal insulation and cryogenic thermal insulation applications including, for example, advanced space suits developed by NASA. Aerogels, as that term is used herein, include polymers with pores with less than 50 nanometers in porous diameter. In a process known as sol-gel polymerization, monomers are suspended in solution and react with one another to form a sol, or collection, of colloidal clusters. The larger molecules then become bonded and cross-linked, forming a nearly solid and transparent sol-gel. An aerogel of this type can be produced by carefully drying the sol-gel so that the fragile network does not collapse.
In the textile and/or apparel industry, silica-based aerogel components have been bonded to apparel fabric for uses such as providing additional insulation. Aerogel is the lowest thermal conductive solid in existence; meaning heat transfer through the aerogel is very limited. However, breathability of aerogel is almost non-existent. Furthermore, aerogel, relative to alternative forms of insulation, is less flexible. Methylated silica aerogel blankets were the first form of flexible aerogel used in textiles or garments. These thermal insulating blankets were developed in cooperation between NASA and Aspen Aerogel, and comprise a combination of methylated silica aerogel (a normally brittle substance) with fibers (typically PET or polyester).
One difficulty with using conventional silica aerogels is that the aerogel tends to shed a fine dust, even when supported by a carrier material. If the aerogel material is not properly contained and sealed within a liner assembly, the dust particles may escape the liner and into the atmosphere. While the dust is not harmful, it is extremely hydrophobic and can cause drying out of skin on contact. To prevent release of the dust from a garment, the aerogel has been encapsulated in another material, typically polyurethane. The aerogel insulating layers have been installed by sewing the outskirts of the polyurethane encapsulation to the fabric of the garment. However, polyurethane is not very breathable and does not have a high thermal resistance. Encapsulation also increases the weight and thickness of the garment. Further, if the polyurethane layer were to be punctured, the garment would be ruined, as the aerogel dust would be released and shed over the garment.
NASA has recently developed a new type of aerogel, a polyimide aerogel, which does not shed a dust. Therefore, insulating layers using this new aerogel do not need to be encapsulated for use in a garment. While polyimide aerogel does not shed dust, it still suffers from the breathability and flexibility issues of the earlier silica-based aerogels.
Prior art garments that have utilized aerogel insulating layers have sought to limit the number of insulating panels or sections, preferring to use just a few, large sections. These garments are often inflexible, and suffer from poor thermal performance (overheating, etc.).
Accordingly, it is desirable to have a garment with the thermal benefits of aerogel, but with increased flexibility and breathability relative to prior aerogel garments. In addition, it is desirable to have a thermoregulating garment which uses directly bonded polyimide aerogel sections as an insulating medium.